HI Geoff. As a newbie I can say that 15m was impossible for me a year ago. I could hunt at about 8 to 10M fine, but for example, 12M would seem impossible, like "get me outa here" rather than hanging around hunting. I can honestly say, to add to Spago a Dave's answer, that by diving 3 to 6 times a month for a year, and you'll be mooching around at 15M without trouble. The weighting idea is very bad, for many reasons, is very advanced, and "cheating" a little I feel. Go the hard way: practice..
best of luck, and while training hard, it'll be good to have a buddy nearby, otherwise, stay well within what you find easy...
